Bioelectrically controlled prosthetic member

ABSTRACT

A prosthetic arm has an upper arm member having a stump receiving socket, a forearm member and an elbow unit secured to the upper arm member and pivotally connected to the forearm member. A drive, housed within the elbow unit, includes a reversible direct current permanent magnet torque motor and a transmission including a planetary gear reduction unit, a reverse locking clutch, and a plano-centric unit and the transmission is connected to the forearm member with its output shaft part of the pivotal connection therewith. The forearm member houses a battery pack and the circuitry by which the motor is operated in either direction in response to electromyographic signals that may be picked up from the biceps and triceps by electrodes when attached to the stump and processed to drive the motor in a direction and at a rate dependent on the dominant EMG signals. The locking clutch is operable to hold the arm flexed against a predetermined load and the elbow unit also houses a tachometer to provide a feedback to modify the power supplied to the motor to enhance the controlability of the amputee of flexing velocities.

United States Patent J erard et al.

[ BIOELECTRICALLY CONTROLLED PROSTHETIC MEMBER Inventors: Robert B.Jerard, Brattleboro, Vt.;

Cord W. Ohlenbusch, Hopkinton, Mass Liberty Mutual Insurance Company,Boston, Mass.

Filed: Sept. 7, 1973 Appl. No.: 395,236

[73] Assignee:

US. Cl 3/l.1; 3/l2.3 Int. Cl A6lf l/06; A6lf l/OO Field of Search 3/1.1,1212.3

References Cited UNITED STATES PATENTS 1/1971 Ohlenbusch et al. 3/1.!

Primary Examiner-Ronald L. Frinks [57] ABSTRACT A prosthetic arm has anupper arm member having a stump receiving socket, a forearm member andan elbow unit secured to the upper arm member and pivotally connected tothe forearm member. A drive, housed within the elbow unit, includes areversible direct current permanent magnet torque motor and atransmission including a planetary gear reduction unit, a reverselocking clutch, and a plano-centric unit and the transmission isconnected to the forearm member with its output shaft part of thepivotal connection therewith. The forearm member houses a battery packand the circuitry by which the motor is operated in ei' ther directionin response to electromyographic signals that may be picked up from thebiceps and triceps by electrodes when attached to the stump andprocessed to drive the motor in a direction and at a rate dependent onthe dominant EMG signals. The locking clutch is operable to hold the armflexed against a predetermined load and the elbow unit also houses atachometer to provide a feedback to modify the power supplied to themotor to enhance the controlability of the amputee of flexingvelocities.

21 Claims, 14 Drawing Figures iZUENTEU N- SHEET 10F 8 PMEMEDH 3.883.900

SHEET 2 OF 8 FIG. 4

1 BIOELECTRICALLY CONTROLLED PROSTHETIC MEMBER BACKGROUND OF THEINVENTION For several years, it has been apparent that bioelectriccontrol of prostheses would be highly advantageous as such control couldbe similar to the control of the corresponding body section lost throughamputation. The muscles of the stump produce electrical signals whichcan be sensed directly from the surface of the skin. Such signals arecalled electromyographic signals and are herein often referred to as EMGsignals.

In U.S. Pat. No. 3,557,387 dated Jan. 26, 1971, a joint prosthesis isdetailed in which such signals are effectively utilized to control theflexing of a forearm member with the advantage generally referred toabove. The forearm member housed the motor, the transmission, anelectromechanical brake, and the circuitry while the current demandswere such that the power source had to be external due to its size andweight.

In general, prosthetic arms in which flexing is effected by EMG signalshave had transmissions that were relatively heavy and bulky andadditionally were not as smooth and quiet in operation as desired.Evaluations and suggestions by amputee users have pointed to a need fora decrease in weight and noise and a smaller, less cumbersome batterypack.

It should be here noted that proposals have been made to useplano-centric drives in prosthetic arms. See Livingston S.M., D. I.Crecraft, Design of an Artificial Elbow; an Electromechanical Solution,Control of Artificial Limbs, the Institution of Mechanical Engineers,London 1968.

While plane-centric drives offer advantages in size and strength, theyhave been excessively noisy at high speeds and run very roughly at lowspeeds.

THE PRESENT INVENTION The general objective of the invention is toprovide a jointed prosthesis of appropriate weight and weightdistribution with flexing responsive to EMG signals derived from thestump to which the prosthesis is attached and with the actuatingmechanism, the circuitry, and the power source all contained within theprosthesis.

This general objective is attained by providing a prothesis with a jointunit housing a motor and transmission. The joint unit is secured to onemember with the output shaft of the transmission connected to the othermember in a manner such that said other member is flexed in a directiondependent on the direction in which the motor is operating with thetransmission providing a substantial gear reduction between the motorand the driven shaft and including a reverse locking clutch to enablethe prosthesis to be locked in a flexed Another objective of theinvention is to provide a locking clutch that overcomes problems ofprevious brakes that may be summarized as over-riding load chatter, anobjective attained by providing a clutch that becomes operative as abrake by the jamming of rollers as a consequence of a load but withinstant locking prevented by including in the clutch frictionallyengaged surfaces. The tachometer controlled velocity feedback isoperative to place the motor in operation at a rate commensurate withthat wanted by the ampu- Other objectives of the invention are to enablethe amputee to have better control of flexing velocities and to enablestarting friction to be readily overcome, both objectives attained bythe use of a tachometer coupled to the motor and providing a velocityfeedback effecting appropriate modification of the power input to themotor.

Another objective of the invention is to provide for furtherconservation of power by the use of limit switches arranged to preventovertravel of the flexed member of the prosthesis in either directionand to permit the prosthesis to remain in its fully extended or itsfully flexed position without the motor drawing battery current.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, apreferred embodiment of the invention is shown, and

FIG. 1 is a side view of a prosthetic arm in accordance therewith;

FIG. 2 is an exploded view of the elbow unit showing the componentshoused therein;

FIG. 3 is an exploded view of the transmission showing its components;

FIG. 4 is a section, on an increase in scale, taken lengthwise of theelbow unit along the axis of its connection with the forearm section;

FIG. 5 is a section taken approximately along the indicated line 55 ofFIG. 4 showing the planetary gear- FIG. 6 is a section takenapproximately along the indicated line 6-6 of FIG. 4 showing the reverselocking clutch;

FIG. 7 is a section taken approximately along the indicated line 77 ofFIG. 4;

FIG. 8 is a section taken approximately along the indicated line 88 ofFIG. 4;

FIG. 9 is a block diagram of the mechanical and electrical components;

FIG. 10 is a schematic view of the EMG amplifiers and the EMG signalprocessing;

FIG. 11 is a like view of the signal summer and the velocity feed backamplifier;

FIG. 12 is a like view of the pulse width modulator FIG. 13 is aschematic view of the battery filter; and

FIG. 14 is a like view of the power amplifier.

An artificial arm in accordance with the invention includes, see FIG. 1,a conventional upper arm section generally indicated at 15 with parts ofits attaching harness indicated at 16 and 17. The arm section 15 has anend plate 18 at its distal end.

A forearm section, generally indicated at 19, has a shell 20, shown onlyin phantom, enclosing a frame which consists of sides 21 and 22 insupport of a plate 23 for circuit boards indicated generally at 24 and25 and a front end wall 26 to which a holder 27 is attached, the holder27 providing support for a terminal device, such as the conventionalhook 28. The holder 27 is detachably attached to the end wall 26 and itslength is determined by the forearm length appropriate for each amputee.At their other ends, the sides 21 and 22 have transverselyaligned holes29 and 30, respectively, the hole 29 round and the hole 30 square.Adjacent said other ends, the frame sides 21 and 22 support a holder 31of U-shaped cross section for the support of the battery pack 32'.

The arm sections 15 and 19 are interconnected by a prosthetic elbow unitgenerally indicated at 33 in FIG. 1 and, as shown inFIGS. 2 and 4 it hasa housing formed in two parts, the part 34 and the part 35 clampedtogether by screws 36. A reversible direct current, permanent magnettorque motor, a tachometer,

generally indicated at 37 and 38 respectively, and a transmission laterto be detailed are within the housing. The housing parts 34 and 35 havesurfaces 34A and 35A that are coplanar when the housing is assembled andseat against the upper arm plate 18 with the housing surface 34Aprovided with a threaded stem 34B by which the elbow unit 33 is attachedto the plate 18 of the upper arm section 15. The housing part 35 has aninternal, annular recess 35B for an internally toothed rim gear orcircular spline 39 clamped between the housing parts 34 and 35 and heldagainst turning relative thereto as by the screws 36.

The drive shaft 40 of the transmission is rotatable in the end wall ofthe housing part 34 and has an outwardly disposed square hub 40A fittingthe square hole 30 of the frame side 21 which is locked thereto by ascrew 41 and an interposed washer 42. The housing part 35 has anchoredtherein an outwardly disposed axial, internally threaded insert 43extending through the hole 29 of the frame side 22 and locked thereto bya screw 44. On both sides of the unit 33 there is a stop 45 engageableby the proximate frame end to limit the extent to which the forearmsection 19 can be flexed or straightened. In practice, the arc throughwhich the forearm section may swing is 130.

The drive shaft 40 has a flange 40B at its inner end clamped to the endwall of the casing 46 of the motor 37 and the interposed end wall of theflexible spline 47 by screws 48. At its other end, the spline 47 has aseries of lengthwise teeth or splines 49 meshing with the rim gear orfixed spline 39 in a manner subsequently detailed.

Within the casing 46 is the stator 50, the brush ring 51 and the rotor52 of the motor 37 with the ends of the rotor shaft 53 supported by ballbearing units 54, one fixed in the end wall of the motor casing 46 andthe other in its end cap 55 which with an internally toothed ring gear56 and an outer clutch housing 57 are clamped to the open end of thecasing 46 by screws 58.

The end of the drive shaft 40 and the end wall of the motor casing 46have sockets defining a chamber 59 for the tachometer 38 whose coupler60 is entrant of a bore 53A on the proximate end of the motor shaft 53and establishes a rigid coupling therewith.

The planetary gear reduction unit or section of the transmission, seeFIGS. 4 and 5, includes the ring gear 56, a clutch housing 61 having aflange 61A clamped between the ring gear 56 and the outer clutch housing57. A rotatable circular input plate 62 has a series of gears 63rotatably mounted thereon each in mesh with the drive gear 64 fixed onthe end of the drive shaft 53 of the motor 37 that extends through theend cap 55 and with the fixed ring gear 56 so that the input plate 62rotates at a desirably reduced rate in either direction in which themotor is operated. In practice and by way of example, the ratio is4.33:1. The input plate 62 has a stub shaft 65 entrant of a socket inthe shaft 66 of a square output cam 67 which is a free fit within thehousing 61, the shaft 66 running in ball bearing units 68 in the hub ofthe clutch housing 61.

The input plate 62 has two diametrically opposed pairs of drive portions69 and 70, see FIG. 6, that are spaced apart with their outer surfacesarcuate and litting freely within the housing 61 and their innersurfaces parallel to and receiving between them opposite sides of theoutput cam 67 and spaced relative thereto to provide a drivingconnection therewith. The arcuate extent of the portions 70 is greaterthan that of the portions 69 and a roller 71 is freely confined betweenthe drive portions 69 and 70 of each pair.

The transmission also includes a low ratio planocentric drive, see FIGS.7 and 8, shown as a Harmonic Drive generally of the type disclosed inUS. Pat. No. 2,906,143 and manufactured by USM Corp. of Boston, Mass.The drive has a flanged output hub 72 pinned to the shaft 66 andtransversely slotted as at 73 to loosely receive the internallydisposed, transversely aligned splines 74 in the bore of a coupling 75having a flange 76 and held in place by a retaining ring keeper 77 onthe end of the hub 72. The coupling 75 has oppositely disposed externalsplines 78 each to fit the recess between the ends of circumferentiallyextending internal ribs 79 at one end of the wave generator plug 80whose outer surface is elliptical as is apparent from FIG. 7. A ballbearing unit 81 has its races so made that the open end of the flexiblespline 47 is thus made sufficiently elliptical to cause its splines 48to move into engagement with the internally toothed rim gear or circularfixed spline 39 in two opposed zones as is characteristic of such adrive, which in practice, provides a reduction in the order of 64:1.

With this transmission, when the motor 37 is operated to raise theforearm section 19, the input cam portion 69 drives to the output cam 67counterclockwise with the rollers 71 held so that they cannot becomejammed against the housing 61. Similarly, when the motor 37 is reversedto lower the forearm section 19, the input cam portion 70 drives theoutput cam 67 clockwise, after the input cam portion 69 first dislodgesthe rollers 71 if they have become jammed. If the arm is driving themotor 37 counterclockwise, the output cam 67 drives the input camportion 70 and the rollers 71 cannot jam.

If, however, the forearm 19 is in a partly flexed position, whether ornot in support of a load, the output cam 67 is biased in a clockwisedirection thereby forcing the rollers 71 to become jammed against thehousing 61. As stated earlier, the housing flange 61 is clamped againstthe ring gear 56 by the outer clutch housing 57 thereby to providefrictional resistance against the turning of the housing 61 unless theload exceeds a predetermined value and should it move, the tachometer 38senses such movement to bring the motor 37 back in service. i

'The main problem with reverse-locking clutches occurs with anover-riding load. For example, if the amputee wishes to lower a heavyload, two problems are present. The first of these is that when theinput cams 69 unjam the rollers 71, the forearm section 19 instantlystarts to take off" in the down direction with both the load and themotor 37 driving it. This effect is minimized by virtue of the fact thejamming angle is not less than l2.l4 nor more than 15.l4 which keeps themotor torque necessary to unjam the rollers 71 to a minimum. Thetachometer 38 then provides the velocity feedback necessary to reducethe power to the motor 37 to prevent the take off.

The second problem results from the fact that the output cam 67, beingunsupported and free to move in the-same direction as the input cams aretravelling, now jams the rollers 71 back against the housing 61. Theinput cams 69 immediately unjam the rollers 71 and the repeated jammingand unjamming results in a chatter effect as the amputee lowers theload. This effect is made minimal by the fact that the drive flange 61Ais frictionally held by the pressure of the flange of the outer housing57 as a disc brake, permitting a degree of slippage with chattereliminated in the case of light to moderate loads and minimized in thecase of heavy loads.

The overall functioning of the electronic circuitry is essentially thesame as described in U.S. Pat. No. 3,557,387 but is quite different inorder to achieve several additional desirable features. These featuresare lower power consumption, better common mode rejection, theincorporation of several deadbands whose use is subsequently describedand better reliability. The overall functioning of this embodiment isdescribed only generally in connection with, FIG. 9. The batteries ofthe pack 32 are of 6 volts and of the nickel cadmium type and providedwith a columbmeter 82 to allow the battery or batteries to be quicklyrecharged and the battery leads to the power amplifier 83 are under thecontrol of a manually operated switch 84. Normally closed limit switches85 and 86 are provided and these are positioned so that the switch 85 isopened when the arm is fully raised or flexed and the switch 86 is openwhen the arm is fully lowered or straightened.

In brief, in the case of the prosthetic arm herein described, the EMGsignals are derived from the biceps and triceps by electrodes held incontact with the skin of the stump overlying those muscles. Such signalsare alternating and relatively weak and must be rectified and suitablyamplified. The circuit sections for thus processing EMG signals derivedfrom the biceps and triceps are indicated at 87 and 88, respectively,see FIG. 10.

The electrical energy is applied to the motor 37 in pulses with theirwidth determining the voltage signal to the motor. The polarity of thevoltage input to the motor 37 and the width of the pulse is determinedby EMG signals and the pulse amplitude is determined by the battery 32.

The processed signals are combined in a summer, generally indicated at89 and schematically detailed in FIG. 11 to provide a difference voltageorsignal representative of the strength difference between the processedinput EMG signals. By way of example, the difference velocity is zerowhen the bicep and tricep signals are of equal magnitude. If the signalderived from the bicep is the larger, the prosthesis is flexed and ifthe tricep signals are the larger, a reverse or straightening movementresults. Such combined signals are further processed by an amplifier 83,see FIG. 14, after modification by a pulse width modulator 90, see FIG.12.

The tachometer 38 has its feedback connected to the summer 89 to providea signal proportional to the rate of movement, see FIG. 12.Reference'has already been made to the use of the velocity feedback toreduce the power to the motor 37 when a heavy load is being lowered. Thevelocity feedback from the tachometer 38 subtracts from the processed.EMG signals and acts to overcome the effect of the non-linearities inthe friction of the mechanical drive system.

Below follows a detailed description of the electronic circuitry asshown in FIG. 10 through FIG. 14. Since the signal amplification andprocessing is the same for both the biceps and triceps, only the bicepschannel is detailed but with the corresponding components of the tricepschannel distinguished by the suffix addition vA to the appropriatereference numerals. The two biceps electrodes 92 and 93 pick up the EMGsignal from the biceps muscle surface from where it is conducted intoamplifiers 94 and 95. These amplifiers are unity gain followers andpresent a very high input impedance to the electrodes. The inputs ofeach of the amplifiers 94 and 95 are protected from excessive voltagesurges by a resistor 96 in conjunction with diodes 97 and 98 and saidamplifier is stabilized against oscillation by a capacitor 99.

The output of each of the amplifiers 94 and95 feeds into an amplifier100, the output of the amplifier 94 with a positive sign and the outputof the amplifier 95 with a negative sign. Thus the amplifier 100amplifies only the difference between these two signals and rejects anysignal that is common to-both of them. The voltage gain of amplifier 100is 10 while the common mode rejection is 60 dB. The gain of amplifier100 is set by resistors 101, 102, 103, and 104. Means are provided topermit trimming of the resistors 101 or 102 to improve the common moderejection beyond 60 dB. Capacitor 106 stabilizes the amplifier 100 whoseoutput feeds through the capacitor 107 and the resistor 108 and intoamplifier 109.

The amplifier 109 serves several functions. It provides a high gain ofup to 5,000 and filters out undesirable frequencies. Filtering networksare the capacitors 107 and 110 and the resistors 108, 111, and 112 andthe capacitors 113, 114, and 115. Maximum gain of this amplifier stageis determined by the resistors 108, 116, 117, I18, and 111 and theresistor 118 is adjustable to permit some gain control. The output ofthe amplifier 109 is an AC signal proportional to the biceps EMG signalbut amplified about 40,000 times. The same processing occurs in thetriceps EMG amplifier and the amplified triceps EMG signal appears atthe output of amplifier 109A.

Rectification of these two signals is accomplished by diodes 119, 120,121, and 122 in conjunction with the amplifier 123. The bicep signal isfull wave rectified with a positive sign and the triceps is full waverectified with a negative sign. Since both rectified signals feed intoamplifier 123 its output produces the difference of these two signals.The output voltage is positive if the biceps EMG signal is stronger, theoutput is negative if the triceps EMG signal is stronger and the outputis zero if both biceps and triceps signals have the same strength.Resistors 124 and 125, and capacitors 126 and 127 set the gain ofamplifier 123 to 10 and provide filtering of any AC ripple remaining onthe rectified signal. The capacitor 128 stabilizes the amplifier 123.The diodes 119, 120, 121, and 122 also provide some incidental deadbandeffect due to the nonlinear characteristics of a semi-conductor diode.The deadband discriminates against 60 Hz interference signals because itis sensitive to the peak value of voltage. 6OHZ interference signals areessentially sinusoidal in shape while EMG signals contain many voltagespikes. Thus for the same voltage average of 60 Hz and EMG the EMG willhave much higher voltage spikes the tips of which would pass through thedeadband while the 60 Hz sinewave amplitude would not be high enough.This and other deadbands will be described later.

FIG. 11 shows the circuitry required for the nonlinear filter, thevelocity amplifier, and the summary amplifier of the summer 89.

The EMG signal contains a large amount of random amplitude variationeven if the muscles producing the signals are under relatively constanttension. Since it is desirable to hold the elbow stationary for sometasks,

and fast amplitude variations improves the control of i the elbowappreciably. The filter uses the nonlinear V-I characteristics of diodes 129, 130, 131, and 132 in conjunction with a capacitor 133. Anamplifier 134 is used as a unity gain follower providing very smallloading for the filter. The time constant of the filter is determined bythe effective resistance of the diodes which in turn depend on the diodecurrent. For sudden large input voltage changes the diode current ishigh and the resulting time constant will be small. For a small and slowinput voltage variation, the time constant is large. Upper and lowerlimits on the time costant are provided by the resistances 134 and 135.The amplifier is stabilized by' a capacitor 137. A second deadband isproduced by the diodes 138 and 139. a

The velocity signal amplifier 140 receives its input signal from thetachometer38. The amplifier l40has a gain of one-half which is set byresistors 141 and 142 and a capacitor 143 stabilizes the amplifier 140.

The summing amplifier 144 of the summer 89 combines the processed EMGsignal and the velocity signal in the proper proportion as determined bythe resistors 145 and 146 and a resistor 147 sets the gain of the amplifier 144 and the capacitor 148 stabilizes it.

The power amplifier 83 receives the signal from the summing amplifier144 and drives the torque motor 37 proportionately. To minimize powerlosses in the power amplifier 90, it operates in a switching mode. Itsoutputs are voltage pulses of constant amplitude and repetition rate butvarying in width according to the input signal. The amplifier 83 can beseparated into sections having functions: (1) the pulse width modulator90A, see FIG. 12, (2) the polarity sensor, (3) the power switchingamplifier, the circuitry shown in FIG. 14.

FIG. 12 shows the circuitry necessary to convert the output of thesumming amplifier 144 of FIG. 11 into the pulse width modulated signalrequired to drive the motor 37. To simplify the switching amplifier andpulse width modulator design, the output from summing amplifier 144 issplit into an unidirectional amplitude signal and a polarity signal. Theamplitude is pulse width modulated, while thepolarity signal determinesthe direction of current through the motor. Both of these functions areaccomplished with the amplifier 145. A-

unidirectional amplitude signal is obtained by rectifying the incomingsignal from the summing amplifier 144 output. The rectification isobtained by the diode 146 and the use of the base-emitter diode of atransistor 147. These two diodes create a half wave rectified signal atthe junction of the diode 146 and a resistor 148. Full waverectification of the signal occurs at the junction of the resistors 149and 150. Resistors 151 and 148 set the gain of amplifier and thecapacitor 152 stabilizes amplifier 145.

The polarity signal is generated by transistor 147. When thebase-emitter diode of the transistor 147 conducts, i.e., when the inputto the amplifier 145 is positive a current will flow in the resistor153, turning on the transistor 154 and causing signal P+ to go positive.At the same time signal P- will go towards ground. When'the input signalto the amplifier 145 is negative the current through the base-emitterdiode of the transistor 147 will go to zero and will cut off, lettingpoint P- rise toward +5V and causing P+ to fall to ground potential. Aresistor 155 provides a path for the base leakage current of thetransistor 154 while the resistor 156 acts as the collector resistor.

Pulse width modulation is accomplished by the amplifier 157 whichcompares the rectified output of the amplifier 145 with a triangularwave generated by the amplifiers 158 and 159 When the triangular signalexceeds the rectified signal the output of the amplifier 157 will benegative. When the. rectified signal exceeds the triangular wave theoutput of the amplifier 157 .Will be positive. The output of theamplifier 157 will thus be a square wave of constant amplitude, with thesame frequency as the triangular wave and a pulse width proportional tothe amplitude of the rectified signal.

.The triangular signal is generated by the amplifier 158 which is anintegrator and by the amplifier 159 which is a comparator, the formerusing a resistor 160 and a capacitor 161 to generate a ramp whose slopedepends on the polarity of the current flowing through the resistor'160.When the voltage at the output .of the comparator amplifier 159 ispositive, current will flow into terminal No. -2 of the amplifier 157and the ramp will have a negative slope. The output of the amplifier 157is compared against a signal derived from the output of the amplifier159 through resistors 162, 163, and 164 and diode 165. When the rampsignal falls below the reference voltage level established by theresistors 163 and 164 and the diode 165, the comparator 159 will switchto a negative and cause a negative reference voltage level and alsoreverse the direction of the current in the resistor 160. The triangularsignal excursion extends from0 volts to some positive level with itszero level determined by the resistors 163 and 164 and the diode 165.This switches the integrated signal from a negative to a positive slopewith the output of the amplifier 158 rising. When the output of theamplifier 158 rising. When the output of the amplifier 158 overcomes thereference voltage the output of the amplifier 159 will switchpositiveagain and the cycle will repeat. Thus the output of amplifier 15 becomesa triangular signal. A resistor 166 provides a matching input impedancefor the terminal No. 3 of the amplifier 159 while a capacitor 167stabilizes the amplifier. The resistor 163 establishes a negative biasfor the reference voltage of the amplifier 159. This creates a deadbandfor the pulse width modulator. Resistors 168 and 169 adjust theamplituce of the triangular signal to its proper level.

In FIG. 13, a battery filter is shown having resistors 170 and 171 andcapacitors 172 and 173 to filter the battery voltage to prevent noisefrom entering the operational amplifier circuits.

The switching amplifier 83 shown in more detail in FIG. 14 must servetwo functions. It must control the total power applied to the motor 37,i.e., the elbow torque and it must also control the polarity of thispower, i.e., the direction of the torque. Power flowing into the motor37 is controlled by four power transistors which operate in pairs. Whenthe transistors 174 and 175 are conducting the motor 37 will drive theelbow unit 33 in a flexing direction. When the transistors 176 and 177are turned on, the motor 37 will drive the unit 33 to extend orstraighten the forearm 19. A flip-flop comprised of transistors 175 and178 decides which power transistor pair controls the motor power. Actionof the flip-flop will be described later.

The amplitude of the motor current is controlled by the on-time of thepower transistors which again is a function of the pulse width modulatorsignal derived from the output of the amplifier 157, see FIG. 12, and isapplied through the resistor 180 to the base of the transistor 181. Whenthis signal is positive, the transistor will turn on pulling resistors182 and 183 to ground. This will turn on the transistor 184 or thetransistor 185 depending on the state of the flip-flop. Assume that thetransistor 184 turns on, the current will flow through the resistor 186and the transistor 187 will turn on to turn on the transistor 187directly and the transistor 174 through the resistor 188. Resistors 189,190, 191, 192, 193, 194, and 195 are base leakage resistors. Resistors186, 196, 197, and 188 limit the current flow. Diodes 198, 199, 200, and201 are flyback diodes which provide for continuity of the currentthrough the motor inductance during the switching interval thusprotecting the power transistors from high voltage spikes.

The flip-flop, the transistors 175 and 178, is clocked or toggled by theleading edge of the pulse width modulator signal and its direction oftoggle is determined by the state of the polarity signals P+ and P. IfP+ is positive and P- is at ground potential every clock pulse will turnoff transistor 175 which will turn on the transistor 178. If this wasthe state of the flip-flop before the clock pulse arrived no action willtake place. If the transistor 17 was turned on and the transistor 179was turned off before the clock pulse arrived, the clock pulse willtoggle the flip-flop into its new state. Reversal of the polaritysignals will cause the opposite behavior. Resistors 202 and 203 providebase leakage paths. Resistors 204 and 205 are the collector resistorsfor the transistors 175 and 178, respectively. Resistors 206 and 207provide the cross-coupling between the transistors 175 and 178. Thegating and trigger circuits uitlize resistors 208, 209, diodes 210, 211,212, and 213, and

Necessary to the objective of providing a jointed prosthesis ofappropriate weight and weight distribution is a reduction in the weightof the battery pack and the recognition of the concept that, rather thanto try to duplicate the action of a natural arm, the effort should bemade to give the amputee the greatest functional capability with theleast inconvenience.

Battery size and weight are determined by work requirements, forexample, the maximum weight that is to be lifted in a predeterminedtime. The use of a purely mechanical, reverse locking clutch instead ofan electro-mechanical brake cut in half the quiescent drain of thesystem and in combination with the improved circuitry, reduced the finalquiescent drain to eleven milliamperes from an original 180milliamperes. As a consequence, the standby operating time increasedfrom 6 to 45 hours despite a reduction in the weight of the batterysource from 3 /2 pounds to about 8 ounces, the maximum lift at 12 inchesto be 5 pounds, and the speed between full flexion and full extension(without load) to be 1.0 second.

Extraneous EMG signals are, however, produced unconsciously by theamputee and these can easily produce momentary current drains in excessof 350 milliamperes making it essential to introduce a deadband into thesignal processing system. Without such a deadband, current is deliveredto the motor as a result of such extraneous EMG signals although themotor does not run as the motor does not produce enough torque toovercome starting friction. The object of the deadband is to provide, inbrief, that zero effort provides zero current to the motor.

While the diodes 119, 120, 121, and 122 of the amplifier 123incidentally delete some of the extraneous EMG signals an additionaldeadband is necessary for the effective control of such extraneous EMGsignals. An effective deadband is, accordingly, provided before thesummer 144 by the parallel diodes 138 and 139.

A problem requiring an additional or second deadband is that DC driftand noise create signals from the junction where EMG and velocityfeedback signals are summed by the amplifier 144. This additionaldeadband is found in the pulse modulator stage. The triangular signalexcursion in the generation of triangular waves extends from aboutOvolts to some positive level and its lower point is determined by thecombination of the resistors 163 and 164 and the diode 165. The resistor163 biases the zero point to a positive value to eliminate the lower 10percent of the summing voltage thereby providing a deadband to preventsmall variations that might occur about the zero level.

The assignment of proper values of the second deadband is difficult dueto conflicting requirements within the feedback loop of the system. Onthe one hand, it is desirable to make the deadband as small as possibleto minimize its effect on the control of the arm. At the same time, themaximum allowable plant gain is directly determined by the magnitude ofthe deadband with a larger gain value resulting in the system beingstiff with respect to velocity which is desirable as it eliminates theeffect of stick-friction in the mechanical drive system.

A large deadband is desirable for good servo system characteristics. Therelationship between the deadband value and the controlability of thearm is more difficult and is best determined in relationship to themechanical deadband created by thefriction in the system and if lessthan that, say by one-half, the amputee will feel it as a slightincrease in the mechanical deadband without noticeable loss of control.In practice, each deadband is in the neighborhood of percent of themaximum signal levels.

It will thus be appreciated that prosthetic joints in accordance withthe invention are well adapted to meet the varied requirements involvedin providing maximum functional capability with the least inconvenienceto the amputee.

We claim:

1. A prosthesis comprising a first member having a stump receivingsocket and provided with a support at its distal end, a second member, ajoint unit secured to the support of the first member, a pivotalconnection between saidjoint unit and the second member relative to saidfirst member, a drive including a direct current permanent magnet motorand a transmission housed within the unit with the output shaft of thetransmission so connected tosaid second member that said second memberis flexed relative to said first member in a direction dependent on thedirection in which said motor is operating, said transmission includingfirst and second reduction stages and a reverse locking clutch betweensaid stages operable under the conditions that the second member is insupport of a load and the motor is not operating to move the member toraise or lower the load and electric circuitry including said motor, abattery, electrodes attachable to the stump and operable to detect EMGsignals from the stump muscles that were used to flex and straighten theamputees missing joint, and signal processing means operable to convertthe detected signals into signals that operate the motor in thedirection and rate that corresponds to the strength of the dominant EMGsignals.

2. The prosthesis of claim 1 in which the first stage is a planetarygear reduction unit and the second stage is a plano-centric drive.

3. The prosthesis of claim 1 in which the transmission also includes afriction brake that may slip to provide a cushion and the engagement ofthe reverse locking clutch.

4. The prosthesis of claim 1 and a direct current permanent magnettachometer coupled to the motor and operable to provide a signalproportional to the rate at which said second member moves relative tothe first member, the signal processing means includes means to amplifyand convert the signals indicative of flexing to one polarity and thoseindicative of straightening to the other polarity, a summer operable tocombine said signals to provide a difference signal, the tachometerprovides a feedback signal proportional to the rate of flexing velocity,means summing the feedback and the difference signals to decrease thepower input when said rate is greater than that intended by the wearerof the prosthesis, and a pulse width modulation and motor drivingamplifier in which battery circuit determines the amplitude of thepulses.

5. The prosthesis of claim 4 in which the reverse locking clutchincludes a friction brake operable, when a load is being lowered tocushion by slipping the reengagement of the clutch as the motor and theload alternatively release and lock the clutch.

6. The prosthesis of claim 1 in which the circuitry includes deadbandmeans operable to exclude substantially all extraneous signals thatwould, when zero movement of the second member was wanted, cause batterydrain.

7. The prosthesis of claim 6 in which the value of the deadband means isless than the mechaical deadband created by friction of the unit.

8. The prosthesis of claim 1 in which the circuitry includes limitswitches operable at either of the limits to which the second member mayswing to open said circuitry.

9. The prosthesis of claim 1 in which the circuitry including its powersource is housed within the second member.

10. The prosthesis of claim 1 in which the first stage of thetransmission includes an internally toothed ring gear, a gear fast onthe motor drive shaft, and a rotatable member includes planetary gearsin mesh with said ring and drive shaft gears, and the clutch includes ahousing and a driven member, means connecting the housing and the ringgear to the motor casing and a driving connection between the rotatablemember and the driven member of the clutch.

11. The prosthesis of claim 10 in which the driven member of the clutchincludes an output cam having oppositely disposed parallel flats and ashaft, the rotatable member includes oppositely disposed spaced pairs ofconnectors, the pairs receiving said flats freely between them toprovide said driving connection when the motor is in operation, androllers confined freely between the connectors of each pair butpermitting them to become jammed between the clutch housing and theflats when said second member is moved in one direction when the motoris not driving said second member in that direction.

12. The prosthesis of claim 11 in which said one direction is thejoint-straightening direction.

13. The prosthesis of claim 11 in which the clutch housing includes aflange and an outer clutch housing clamps said flange against the faceof the ring gear to an extent providing frictional resistance againstthe flange turning in either direction.

14. The prosthesis of claim 11 in which the second stage is atransmission of the plano-centric type with its driven shaft the outputshaft of the unit, the second stage including a fixed circular spline,the motor, the first stage including a fixed circular spline, the motor,the first stage and the clutch are housed within the second stage andthe motor is connected thereto to rotate therewith. and the fixedcircular spline of the second stage is fixed within the unit. 15. Theprosthesis of claim 11 and a DC PM tachometer coupled to the motor andoperable to provide a signal proportional to the rate of flexingvelocity so that when the rotatable member unjams the rollers and theexternal load on the arm causes the output cam to go in the samedirection the feedback signal prevents the arm from taking off in amannor not intended by the amputee.

16. The prosthesis of claim 11 in which the acute angle which a lineperpendicular to the face of each flat of the output cam and whichpasses through the center of the appropriate roller would make with asecond line also passing through the center of the roller and throughthe point of its tangency to the inside of the housing is no less thanl2.14 and no more than 15. 14 in order to minimize the force required bythe rotatable member to unjam the rollers.

17. The prosthesis of claim 4 and a deadband following thesignal-combining summer providing the difference signals to barextraneous EMG signals, said deadband being in the neighborhood of tenpercent of the maximum signal level.

18. The prosthesis of claim 17 in which the deadband motor drivingamplifier, a triangular wave generator to provide the amplitude of thepulses and having a signal excursion extending from 0 volts to apositive level,

said zero level comprising first and second resistors and a diode, saidfirst resistor comprising the second deadband and biasing said zeropoint to a positive value that eliminates voltage in the neighborhood often percent of the voltage output of said generator.

21. The prosthesis of claim 4 in which the pulse modulating and motordriving amplifier includes two pairs of power transistors, each pair fora particular polarity of the pulse delivered thereto, and a flip-flopoperable to select the appropriate pair of power transistors that is tobe operated to control direction in response to the polarity of thepolarity signals and shiftable only on and at the leading edge of thepulse width modulation pulse.

1. A prosthesis comprising a first member having a stump receivingsocket and provided with a support at its distal end, a second member, ajoint unit secured to the support of the first member, a pivotalconnection between said joint unit and the second member relative tosaid first member, a drive including a direct current permanent magnetmotor and a transmission housed within the unit with the output shaft ofthe transmission so connected to said second member that said secondmember is flexed relative to said first member in a direction dependenton the direction in which said motor is operating, said transmissionincluding first and second reduction stages and a reverse locking clutchbetween said stages operable under the conditions that the second memberis in support of a load and the motor is not operating to move themember to raise or lower the load and electric circuitry including saidmotor, a battery, electrodes attachable to the stump and operable todetect EMG signals from the stump muscles that were used to flex andstraighten the amputee''s missing joint, and signal processing meansoperable to convert the detected signals into signals that operate themotor in the direction and rate that corresponds to the strength of thedominant EMG signals.
 2. The prosthesis of claim 1 in which the firststage is a planetary gear reduction unit and the second stage is aplano-centric drive.
 3. The prosthesis of claim 1 in which thetransmission also includes a friction brake that may slip to provide acushion and the engagement of the reverse locking clutch.
 4. Theprosthesis of claim 1 and a direct current permanent magnet tachometercoupled to the motor and operable to provide a signal proportional tothe rate at which said second member moves relative to the first member,the signal processing means includes means to amplify and convert thesignals indicative of flexing to one polarity and those indicative ofstraightening to the other polarity, a summer operable to combine saidsignals to provide a difference signal, the tachometer provides afeedback signal proportional to the rate of flexing velocity, meanssumming the feedback and the difference signals to decrease the powerinput when said rate is greater than that intended by the wearer of theprosthesis, and a pulse width modulation and motor driving amplifier inwhich battery circuit determines the amplitude of the pulses.
 5. Theprosthesis of claim 4 in which the reverse locking clutch includes afriction brake operable, when a load is beiNg lowered to cushion byslipping the reengagement of the clutch as the motor and the loadalternatively release and lock the clutch.
 6. The prosthesis of claim 1in which the circuitry includes deadband means operable to excludesubstantially all extraneous signals that would, when zero movement ofthe second member was wanted, cause battery drain.
 7. The prosthesis ofclaim 6 in which the value of the deadband means is less than themechaical deadband created by friction of the unit.
 8. The prosthesis ofclaim 1 in which the circuitry includes limit switches operable ateither of the limits to which the second member may swing to open saidcircuitry.
 9. The prosthesis of claim 1 in which the circuitry includingits power source is housed within the second member.
 10. The prosthesisof claim 1 in which the first stage of the transmission includes aninternally toothed ring gear, a gear fast on the motor drive shaft, anda rotatable member includes planetary gears in mesh with said ring anddrive shaft gears, and the clutch includes a housing and a drivenmember, means connecting the housing and the ring gear to the motorcasing and a driving connection between the rotatable member and thedriven member of the clutch.
 11. The prosthesis of claim 10 in which thedriven member of the clutch includes an output cam having oppositelydisposed parallel flats and a shaft, the rotatable member includesoppositely disposed spaced pairs of connectors, the pairs receiving saidflats freely between them to provide said driving connection when themotor is in operation, and rollers confined freely between theconnectors of each pair but permitting them to become jammed between theclutch housing and the flats when said second member is moved in onedirection when the motor is not driving said second member in thatdirection.
 12. The prosthesis of claim 11 in which said one direction isthe joint-straightening direction.
 13. The prosthesis of claim 11 inwhich the clutch housing includes a flange and an outer clutch housingclamps said flange against the face of the ring gear to an extentproviding frictional resistance against the flange turning in eitherdirection.
 14. The prosthesis of claim 11 in which the second stage is atransmission of the plano-centric type with its driven shaft the outputshaft of the unit, the second stage including a fixed circular spline,the motor, the first stage including a fixed circular spline, the motor,the first stage and the clutch are housed within the second stage andthe motor is connected thereto to rotate therewith, and the fixedcircular spline of the second stage is fixed within the unit.
 15. Theprosthesis of claim 11 and a DC PM tachometer coupled to the motor andoperable to provide a signal proportional to the rate of flexingvelocity so that when the rotatable member unjams the rollers and theexternal load on the arm causes the output cam to go in the samedirection the feedback signal prevents the arm from ''''taking off''''in a mannor not intended by the amputee.
 16. The prosthesis of claim 11in which the acute angle which a line perpendicular to the face of eachflat of the output cam and which passes through the center of theappropriate roller would make with a second line also passing throughthe center of the roller and through the point of its tangency to theinside of the housing is no less than 12.14* and no more than 15.14* inorder to minimize the force required by the rotatable member to unjamthe rollers.
 17. The prosthesis of claim 4 and a deadband following thesignal-combining summer providing the difference signals to barextraneous EMG signals, said deadband being in the neighborhood of tenpercent of the maximum signal level.
 18. The prosthesis of claim 17 inwhich the deadband comprises parallel opposite diodes in front of themeans summing velocity feedback signals and the EMG difference signals.19. The prosthesis of claim 17 anD a second deadband to eliminate DCdrift and noise incidental to the second summing, said second deadbandbeing incorporated in the circuitry before the pulse width modulatingand motor driving amplifier and being in the neighborhood of ten percentof the maximum signal level.
 20. The prosthesis of claim 19 in which thecircuitry includes as part of the pulse width modulating and motordriving amplifier, a triangular wave generator to provide the amplitudeof the pulses and having a signal excursion extending from 0 volts to apositive level, said zero level comprising first and second resistorsand a diode, said first resistor comprising the second deadband andbiasing said zero point to a positive value that eliminates voltage inthe neighborhood of ten percent of the voltage output of said generator.21. The prosthesis of claim 4 in which the pulse modulating and motordriving amplifier includes two pairs of power transistors, each pair fora particular polarity of the pulse delivered thereto, and a flip-flopoperable to select the appropriate pair of power transistors that is tobe operated to control direction in response to the polarity of thepolarity signals and shiftable only on and at the leading edge of thepulse width modulation pulse.